Field of the Invention
The present invention relates to a projection type image display apparatus, a method for displaying a projection image, and a storage medium. In particular, the present invention is suitable for use in forming a multiscreen display in which images projected from a plurality of projection type image display apparatuses onto the multiscreen display include an overlap area.
Description of the Related Art
Conventionally, a multiscreen display has been formed using images projected from a plurality of projection type image display apparatuses. To form a multiscreen display in this way, adjacent images among images projected from a plurality of projection type image display apparatuses are arranged to include an overlapping image area, and luminance correction is performed on image signals of the overlapping image area to make seams of the adjacent images less noticeable. Furthermore, the overlapping image area is arranged to have a predetermined width, so that even if characteristics such as luminance and color slightly differ between the projection type image display apparatuses, the differences in the characteristics are less visible. Hereinafter, an “overlapping image area” will be referred to as an “image overlap area” as needed.
Among the projection type image display apparatuses, a transmission type image display apparatus and a reflection type image display apparatus cannot completely block transmitted light and reflected light, respectively. Thus, when a black is displayed in an image projected from a projection type image display apparatus, the black has a slight luminance. Therefore, when the black is displayed in a multiscreen display, the luminance of an effective image in an image overlap area becomes higher than the luminance of an effective image in areas outside the image overlap area. This causes seams of the image overlap area and the areas outside the image overlap area to be visually recognized.
In view of the foregoing, Japanese Patent Application Laid-Open No. 2002-268625 discusses a technique in which an offset (correction value) is added to signals of an effective image in areas outside an image overlap area for each projection type image display apparatus to realize an entirely uniform black display.
However, if the correction value is uniformly added to all gradations, luminance saturation occurs in high gradation areas. Furthermore, when an image on a display that has undergone gamma (γ) correction is viewed, a luminance discontinuity becomes visibly recognizable in the high gradation areas.
A possible method for avoiding luminance saturation may be a method in which the correction value is set to be 0 at the highest gradation. However, even with this method, the luminance discontinuity in intermediate gradation areas that occurs when an image on a display that has undergone gamma (γ) correction is viewed, cannot be overcome.